PS 78-156 - Reintroduction of prescribed fire to a long unburned Cypripedium montanum population on the Modoc National Forest, California

Friday, August 11, 2017
Exhibit Hall, Oregon Convention Center
Becky L. Estes, Pacific Southwest Region, USDA, Placerville, CA, Eric E. Knapp, Pacific Southwest Research Station, USDA Forest Service, Redding, CA and Carl Skinner, Pacific Southwest Research Station, USDA Forest Service
Background/Question/Methods

Cypripedium montanum is wide ranging plant found in isolated populations throughout Northwest California. C. montanum is characterized by a shallow rhizome and as such is potentially vulnerable to high severity fire. As a result, fuels management, especially the application of fire, is often avoided. However, the presence of fire scarred trees in close proximity to C. montanum plants suggests that populations were once exposed and were likely resilient to low severity fire. In order to determine the effect of fire on the plants, prescribed burning treatments were conducted in plots (≈78.5 m²) in June 2010 (spring) and September 2010 (fall). Pre and post fire and fuel characteristics were observed. In addition, percent cover of all forbs, shrubs, and trees (< 1.5m) were recorded. Temperature and residence time were measured using thermocouples at the surface and 2.5, 5 and 10cm from the top of the forest floor. In order to determine the effects of both seasons of prescribed fire on the plants, location, life-stage, growth, and reproductive effort of all C. montanum stems were recorded. Repeated measures ANOVA was used to test hypotheses regarding the effects between spring and fall prescribed fire treatments and the controls on census, phenology and vigor.

Results/Conclusions

Fuel loading and duff consumption were greater in the spring burns, although a greater amount of large diameter fuels were consumed in the fall burns due in part to lower fuel moisture. No peak differences in temperature were noted at the surface, but residence time that exceeded 60°C (threshold for cellular death) was greater in the spring burns. Maximum temperature was higher and residence longer in the forest floor during the spring burns which correlated with lower duff moisture content. No differences in the heat pulse into the soil at either 5 or 10cm were noted as soil moisture was nearly equivalent. Initial declines in percent flowering were observed in burned plots the following growing season, but by 5 years post burn all treatments were nearly equivalent. No differences in number of plants or stems were observed in the control or burned plots in any sampling year. Reintroduction of low severity fire was not found to be detrimental to the C. montanum plants and may prove to be an effective treatment to avoid high severity wildfire in the future.